The prior art shows various type of dampers with and without spring means to hold the cap away from the frame in or on the chimney flue when not in use. For instance, U.S. Pat. No. 5,125,869 granted on Jun. 30, 1992, and U.S. Pat. No. 5,556,329 granted on Sep. 17, 1996 disclose a conventional spring biased chimney damper.
Typically, these prior art devices include a frame defining an open window area, a cap for selectively covering and uncovering the open window area, and spring means inter connecting the cap and frame and biasing the cap to it's open position. The springs are multi-component and connected to the frame outside of the window area. There may be a poorly designed alignment means to align the cap over the window opening as it is operative only the final phase of it's movement to the closed position. No means is provided for selectively adjusting the spacing between the cap and the frame in the cap open position.
Some chimney dampers include a lock mechanism to keep the damper in an open position in case of a chimney fire comprising a fusible link connected to spring means and in case of over heating, due to for example a chimney fire, the link melts causing the spring to move into a position in which it locks the cap in an open position. This fusible link must be replaced after each occurrence of overheating and because of the in use position of the damper on top of the chimney it is difficult to replace.
Moreover, some chimney damper embodiments require that the cap turn a quarter turn during each of the closing and opening movements. In another embodiment, the cap does not rotate and is captive in an outer skeleton frame limiting movement of the cap to reciprocal movement only wherein the spring system is connected to a plate that can move reciprocally on a shaft as well as rotate on that shaft.